Pervoskites compounds have been widely studied because of their interesting chemical, electrochemical and electronic properties. They are adapted to a number of applications such as in nonvolatile memories, photoelectrochemical cells, thin-film capacitors, and non-linear optics [1-4]. Recently, there has been growing interest in the use of near infrared (780-2500 nm) absorbing pervoskite materials in solar heat shielding applications. Tungsten trioxide (WO3) possesses a wide band gap that ranges from 2.6 to 3.0 eV [5, 6] and they are transparent in visible and near infrared (NIR) light. However, a strong NIR absorption property could be achieved using systematic induction of free electrons into WO3 crystal by ternary elements addition [7, 8]. In recent studies, the nanosized metal doped tungsten oxides (MxWO3, where 0.1<x<1), termed as tungsten bronze, has emerged as a promising material for numerous applications such as solar heat-shielding [8, 9], electrochromic devices [10] and biomedical study [11]. Cesium tungsten bronze (Cs0.33WO3) among other metal tungsten bronze nanoparticles have shown an excellent absorption in near infrared (NIR) spectral region (700-3,000 nm) with high optical transparency in the visible spectral region (380-700 nm) [8, 9, 12]. Tungsten bronze provides a superior NIR absorption in comparison to other transparent conductive oxides, such as tin doped indium oxide (ITO), antimony doped tin oxide (ATO), and non-transparent deeply colored lanthanum hexaboride (LaB6) [13-15]. The reasons behind the origin of remarkable NIR absorption by CsxWO3 (x=0.15, 0.25, and 0.33) as well as WO2.72 was investigated using Mie scattering theory by Adachi and Asahi [14]. The paper reported that the localized surface plasmon resonance and polarons of localized electrons contribute to NIR absorption of cesium tungsten bronze nanoparticles.
In recent years, NIR shielding Cs0.33WO3 had been synthesized mainly by two methods: solid state reaction [8, 14, 15] and high pressure wet-chemical routes (solvothermal and hydrothermal) [9, 10, 12, 16, 17]. Other reported synthesis methods include, stirred bead milling process [11] and inductively coupled thermal plasma technology [13]. The widely used, traditional solid state reaction method requires high temperature and harsh reaction conditions. The size of nanoparticles is often not well controlled and the synthesis method requires extra steps which become more tedious for large scale. Furthermore, the reported low reaction temperature methods such as hydrothermal and solvothermal processes require long reaction time (usually more than 20 hour) to obtain homogenous CsxWO3 nanorods.
One of the major challenges in nanoparticle synthesis is developing rational strategies to control size, shape, stoichiometry composition, and structure. In nonaqueous solution routes to metal oxide nanoparticles, like solvothermal process, the role of organic solvent is important in obtaining single-phase products. Benzyl alcohol as solvent has shown an attractive reaction approach for synthesis of homogeneous ternary, multi-metal and doped oxide nanoparticles [19, 23, 24]. It acts as a solvent, ligand and reactant in dissolving precursors, determining reaction pathways, and forming metal oxide, respectively.